1. Field of the Invention
In general, the present invention relates to the structure of airport runways. More particularly, the present invention relates to the methods used to create grooving patterns in airport runways.
2. Prior Art Description
Most all paved surfaces are impervious to water. Consequently, any low-point or depression in a paved surface has the potential to cause puddling during a rain storm. Furthermore, if the rate of precipitation excesses the rate at which water can flow off the payment, puddling will inevitably occur. If the paved surface is an airport runway, such puddling can be extremely dangerous. If the wheels of an airplane roll through a puddle during takeoff or landing, the wheels of the airplane can hydroplane. This can cause the airplane to turn on the runway and/or prevent an airplane from stopping or reaching takeoff speeds prior to the end of a runway.
It is for these reasons that many airports cut grooves into the surfaces of the paved runways. According to the U.S. Federal Aviation Administration (FAA), runway grooves should be ¼ inch wide, ¼ inch deep and should be spaced one and a half inches apart. In theory, the grooves provide flow channels for water. Any water on the runway should flow into the grooves and should then flow to the sides of the runway. Furthermore, even if some puddling does occur, the grooves provide room for the water to flow as the wheels of the airplane pass. Consequently, hydroplaning can be avoided.
Traditionally, grooves are cut into the pavement of a runway using a standard diamond embossed cutting blade. The cutting teeth on the blade have a uniform thickness. Consequently, when the blade cuts into the pavement, it produces a groove that has a square or rectangular cross-sectional profile.
Grooves with rectangular cross-sectional profiles are not without disadvantages. Grooves of such a configuration have right-angle top edges where the pavement encounters the cut groove. These sharp edges cause wear to airplane tires as the treads of the tire touch down upon the runway. Likewise, the sharp top edges tend to chip and wear when contacted by airplane wheels, snowplows and other vehicles. Furthermore, due to freeze-thaw cycles and other weathering, the sharp top edges chip and fall away. The chipped material typically falls into the bottom of the groove. This creates small obstructions in the grooves. These small obstructions become a natural catch point for dirt, tire rubber and other debris. Soon, the groove is clogged and cannot effectively channel water. The grooving then becomes an ineffective water channeling device and dangerous puddling can occur.
In the prior art, attempts have been made to produce grooves that do not have rectangular cross-sectional profiles. If a groove can be made with sloped sides, then the sharp top edge can be eliminated. This would cause less wear, less debris and would, therefore, reduce the need for maintenance.
In the prior art, experiments have been conducted on airport runways that have been grooved with V-shaped grooves. A description of such a runway grooving configuration is found in U.S. Pat. No. 5,311,705 to Zuzelo, entitled Contoured Cutting Tool, and in Defense Technical Information Center report AD0692075, entitled Friction Effects Of Runway Grooves, Runway 4R-22L, John F. Kennedy International Airport. Although V-shaped grooves do wear and weather better than rectangular-shaped grooves, they have other disadvantages. Primary among those disadvantages is that a V-shaped groove does not channel water as efficiently as does a rectangular-shaped groove. Accordingly, in order to achieve the same degree of water removal from a runway, either more V-shaped grooves must be cut or deeper V-shaped grooves must be cut. This significantly increases the cost of grooving a runway.
To create a V-shaped groove, a blade is used having teeth with a triangular profile. Such blades do initially create a groove in pavement that is V-shaped. However, the V-shape of the cutting teeth causes the cutting teeth to wear unevenly. Consequently, after a short time, the shape of the groove being cut changes and eventually returns to a rectangular shape. The cutting blades must therefore be replaced very often during cutting. Since the blades contain diamond dust and are very expensive, the cost of cutting non-rectangular grooves soon becomes cost prohibitive.
In order to avoid many of the stated disadvantages of both rectangular grooves and V-shaped grooves, a trapezoidal groove may be produced in a runway. A trapezoidal groove is a groove with a flat bottom and sloped sidewalls. Trapezoidal grooves channel water more efficiently than do rectangular grooves and V-shaped groves. Accordingly, less trapezoidal grooves are needed to move the same amount of water. Accordingly, a lower density of trapezoidal grooves is required. Less trapezoidal grooves results in lower production cost and less maintenance.
The problem with trapezoidal grooving is it previously could not be made in an economically practical fashion. In the prior art, blades have been created that have cutting teeth with trapezoidal shaped profiles. However, when such blades are used to cut concrete, the sides of the cutting teeth quickly wear. Thus, after cutting only a short distance, the groove changes shape and the cutting blade must be replaced.
In U.S. Pat. No. 4,267,814 to Benson, entitled Abrasive Saw Blade For Trapezoidal Grooving, an attempt is made to create a blade that cuts trapezoidal grooves and lasts longer than a traditional blade. In the Benson patent, a blade is made with cutting teeth of alternating shapes. Every other cutting tooth has a standard rectangular-shaped profile. Interposed between the standard cutting teeth are cutting teeth with a trapezoidal-shaped profile. However, the trapezoidal-shaped teeth are wider than the rectangular teeth. As a consequence, the trapezoidal teeth do not fit into the groove cut by the rectangular teeth. The result is that the trapezoidal teeth impact the edges of the groove made by the rectangular teeth. This produces chipping in the walls of the groove and excessive wear in the trapezoidal teeth. Consequently, the blade wears out at least as quickly as blades with all trapezoidal teeth.
A need therefore exists for a runway grooving system and method that wears better than traditional grooving, channels a greater amount of water than traditional grooving, requires less maintenance than traditional grooving and can be made as inexpensively as traditional grooving. This need is met by the present invention as described and claimed below.